Electrical sensing and/or signal application device

ABSTRACT

The electrical signal sensing and/or signal application device for sensing electrical signals on a surface and/or for applying electrical signals to a surface, particularly of human or animal skin or other organs or tissues, comprises a substrate ( 12 ) having first and second major surfaces ( 14 ), and a plurality of electrodes ( 16 ) arranged on the first major surface ( 14 ) of the substrate ( 12 ) and projecting therefrom, each of the electrodes ( 16 ) comprising a pointed contact end ( 36 ) facing away from the substrate ( 12 ) for contacting the surface, and a base end ( 26 ) facing towards the substrate ( 12 ). On the first or second or both major surfaces ( 14 ) of the substrate ( 12 ) there is arranged a plurality of first contact pads ( 22 ) for electrical connection to contact elements of an evaluation and/or driving means for evaluating the sensed electric signals and/or applying signals to the electrodes ( 16 ), the first contact pads ( 22 ) being electrically connected to the electrodes ( 16 ). The first major surface ( 14 ) of the substrate ( 12 ) comprises, for each electrode ( 16 ), a second contact pad ( 18 ) the base ends ( 26 ) of the electrodes electrically and mechanically connected to the second contact pads ( 18 ). Each electrode ( 18 ) is generated by bonding an electrically conductive bonding wire to a second contact pad ( 18 ) for generating a thickened socket portion ( 24 ) of the electrode comprising its base end ( 26 ), and by tearing the bonded bonding wire off the socket portion ( 24 ) so as to generate a pointed portion ( 34 ) of the electrode ( 16 ) comprising its pointed contact end ( 36 ) and projecting from the socket portion ( 24 ) thereof.

FIELD OF THE INVENTION

[0001] The invention relates to an electrical signal sensing and/orsignal application device for sensing electrical signals on a surfaceand/or for applying an electrical signal to a surface. Such a device inparticular is used for sensing electrical signals on and/or for applyingelectrical to human or animal skin and most preferably are used intherapy and diagnostic methods. For example a signal sensing device canbe used to record impedances or other electrical images of tissues andother components or objects to which the sensing device can beelectrically attached. On the other side the device can be used to applyelectric current or voltage for stimulating tissues or other componentsor objects.

[0002] Moreover, the invention relates to a method for manufacturing adevice as described above. Finally, the invention also relates to theuse of such a device for therapy and diagnostic methods.

BACKGROUND OF THE INVENTION

[0003] Medical diagnosis is utilizing diverse approaches of obtainingimages of humans and animals such as X-ray, computer tomography,nuclear-spin-resonance and ultrasonics. The straight forward photographyis of lesser importance as it merely records the external appearance ofskin portions of humans and animals while the other methods presentspecific views especially of the inner portions of the body which aremore suitable for the diagnosis.

[0004] More recently the recording of impedance and other electricalimages was developed. The use of single electrodes including theindependent handling of several electrodes for the recording of theelectrical properties such as the impedance typically as a function oftime is well known for many decades, especially in the fields ofelectro-cardiography (ECG or EKG) and electro-encephalography (EEG). Inthese cases typically the individual electrodes are attached to the skinby some means such as suction devices or adhesives. Furthermore, theseelectrodes are provided with a relatively large surface having the orderof magnitude of about 1 sq. cm which consists of metals, conductive gelsor conductive adhesives. Typically the electrical properties arerecorded as a function of time. However, the recent developmentsutilizes arrays of these electrodes where each of them records theelectrical properties such as the impedance or conductivity in a mannerthat all these values are simultaneously recorded and for examplebrought onto a display like a monitor. This then provides imagesyielding information which is significantly different from the images ofthe other diagnostic methods as stated above. The known specificconfigurations will be referred to in more detail below.

[0005] A particular area of interest is the diagnosis of cancer where itis of interest to investigate the skin primarily related to breastcancer and skin cancer. The article “Overview of Skin Cancer Detectionand Prevention for the Primary Care Physician” by A.3. Bruce et al. ofthe Mayo Clin. Proc. 2000; 75; 491-500 describes the diagnosticpossibilities for a primary evaluation of the skin with respect to thedetection of specific cancers. This article states that the initialvisual inspection by the physician is a meaningful first step in orderto decide whether or not further investigations will be necessary.However, it is desirable after the immediate first visual inspection todevelop another rather simple method for identifying whether or notcancer can be diagnosed.

[0006] WO-A-97/47235 provides a method of a dermal diagnostic analysisthrough the use of a digital camera which allows a somewhat moresophisticated approach through the recording of the critical portions ofthe skin.

[0007] WO-A-98/09155 shows a step further, it includes to apply achemical to the critical skin area and after several hours this area isilluminated with ultraviolet light and the fluorescent irradiation canbe recorded through picturing spectroscopy. This allows to identifycancerous portions of the skin. This method, however, is time consumingand cumbersome and still requires additional diagnostic methods in mostof the cases.

[0008] A number of possibilities have become known which utilize thedetermination of the electrical properties of the skin.

[0009] U.S. Pat. No. 5,928,159 describes an apparatus and methodsutilizing a probe provided with several electrodes which is applied to askin portion that might be cancerous and the electrical data of theseportions are recorded in comparison with a normal neighbour portion ofskin.

[0010] U.S. Pat. No. 5,143,079 describes an apparatus for the detectionof tumors in tissues. It utilizes a probe with a fixed arrangement ofelectrodes, e.g. 64 elements arranged in an 8×8 array. These electrodeshave a hexagonal form, the electrodes being of gold plated printedcopper for example. The hexagons typically have sides of 10 mm. Theseelectrodes by themselves are still rather large so that only a fairlysmall number of them can be utilized in the probe and, therefore, a realimage cannot be generated.

[0011] A further development is described in U.S. Pat. No. 5,810,742 andthe article “T-SCAN™ as a Diagnostic Tool for Breast Cancer” by M.Assenheimer et al. accessible in the Internet throughwww.transscan.co.il/publication1.html. The described systems have afairly large number of individual electrodes allowing to generate animage of having a reasonable resolution. The electrodes described aretypically in a rectangular array with a multiplicity of wells which areseparated by dividers consisting of insulating material. These wells arefilled with a hydro-gel or conductive gel and the wells themselves areprovided with a metal electrode which projects to the portion below theelectrode so that the entire configuration can be applied onto a printedcircuit board (PCB) which has a corresponding array of electrodes. Inthis manner a discardable article is generated. This is of importance asfor well known reasons it is not advisable to use electrodeconfigurations for more than a single patient. The PCB as such has anarray of conductive paths which are guided to a multi-pin connectorwhich then is connected through a cable to the evaluation computer whichis capable of recording the electrical characteristics of eachindividual electrode so that the desired image can be generated in thecomputer and displayed on the monitor. The use of wells filled with aconductive gel has the disadvantage of being difficult to manufacturethus being expensive which is critical for such a discardable article.Furthermore, the spacing between these wells is limited which reducesthe resolution of the desired image. This is of particular importance ascritical skin portions which might be cancerous only have dimensions ofa few millimeters and, therefore, for obtaining a good resolutionpitches of the wells in the order of several tenths of a millimeter arerequired.

[0012] The use of multiple electrodes or arrays of electrodes is wellknown and described in a large number of publications.

[0013] U.S. Pat. No. 3,490,439 describes an assembly of electrodes usedfor electro-encephalography. The electrodes as such are small foam ballscoated with a conductive cloth piece.

[0014] U.S. Pat. No. 5,452,718 presents an electrode configuration inwhich a conductive material having a tip is embedded in a plasticferrule.

[0015] U.S. Pat. No. 3,896,790 relates to a brain wave sensor in which asingle electrode is used which consists of several prongs which ensure agood electrical contact, even in the presence of hair.

[0016] In the above cited references all these electrodes essentiallyare still separate from each other. Configurations are also known inwhich a multiplicity of electrodes is arranged in a fixed mutualconfiguration. This is described for example in U.S. Pat. No. 5,184,620,U.S. Pat. No. 4,353,372 and U.S. Pat. No. 6,055,448. In all these casesthe electrodes are embedded into a common carrier, however, they arestill used for the typical ECG or EEG application which means thatdespite their fixed spacial relationship they are individually used andusually only their time dependence is recorded.

[0017] In all electrodes and electrode arrays described aboveconfigurations are shown in which the electrodes themselves have arelatively large surface and they are typically directly applied to theouter surface of the skin. There are alternative methods of utilizingelectrodes which essentially consist of individual needles. Theseneedles operate in a somewhat different manner. If properly applied theyallow to penetrate the outermost portion of the skin and provide a morevaluable determination of the electrical properties which for therecording of the image appears to be advantageous.

[0018] A needle electrode is described in U.S. Pat. No. 5,482,038 wherean individual sharp needle is inserted into a special holding devicewhich allows to establish a defined pressure. Needles of this type areused for example in neurological examinations using an electro-myograph(EMG).

[0019] Similar configurations can be taken from the references U.S. Pat.No. 5,509,822 and EP-A-0 533 487 which are either used forelectro-myography or for electro-cardiography. These needles are eithera multiplicity of several components that are handled independently butconnected to a common monitoring system or configurations in which apair of needles is used.

[0020] EP-A-0 538 739 describes an array of needles, the number rangingbetween 50 and 150. These needles are brought into a common plasticholder. The needles themselves have a solid configuration with arelatively sharp pin similar to those used in acupuncture. Each needleis provided with a spring allowing to apply all needles with a givenpressure. The array is a pre-determined geometrical configurationtypically having an overall circular circumference. The data, however,are collected individually from each electrode and utilized in some kindof a statistical evaluation. There is no intention to record an image.Furthermore, the reference is silent with respect to the establishmentof the electrical contacts between these needles and the cable leadingto the electronic evaluation unit.

[0021] DE-U-92 18 879 relates to an array of electrodes for thedetermination of the distribution of electrical potentials on the skinof a patient. It shows multiplicities of electrodes for the abovedescribed purpose and the object of this reference is to replace thismultiplicity of electrodes by a foil having semi-conductive layers whichis scanned for example by a laser beam causing a temporary conductivityof a small portion of the foil thus replacing a multiplicity ofelectrodes by such a foil which is scanned through point by point. Noreference is made at all to the type of electrode configurations used.

[0022] DE-U-85 02 291 describes arrays of needle electrodes forbiomedical applications where each electrode is individually connectedto a cable so that a multiplicity of signals can be recorded. Noreference is made to the possibility of recording an electrical image.

[0023] WO-A-78/07825 describes an electrode and the related method ofmanufacture. A base carrier contains an arrangement of conductingprotuberances arising from the base serving as the electrodes. Theseelectrodes are individually connected to an electrical path that isleading to an array of contact areas which allow to transfer the signalto a recording unit. The protuberances or needles have the shape ofcones. These cones are grown on a multi-layer configuration andtypically have dimensions up to 25 microns. This means that they arerelatively small and their primary use is in the area of neurology. Theneedles allow to penetrate the surface of the tissue to be diagnosed.

[0024] U.S. Pat. No. 5,215,088 describes a three-dimensionalmulti-electrode device especially useful as a neuron interface. Theelectrodes are electrically isolated from each other, the signals aretypically transmitted using a multiplexing circuitry. The needlestypically consist of semi-conductive material on the basis of silicon.In a block of such material sequences of cuts are obtained using a sawutilized in the microelectronic industry. This is performed in twodirections so that an array of pins is obtained having a rectangular orsquare cross-section. In a subsequent etching process material is takenaway from the upper portions of these columns so that they obtain aneedle-like form. This is particularly suitable for neuron-typeapplications e.g. a prosthesis for a blind person. The process is rathercomplicated and thus expensive, needle arrays of this configuration donot appear to be suitable as single use throw-away articles because ofthe high cost.

[0025] Arrays of needles as electrodes require to bring them into adefined array by simultaneously electrically isolating them from eachother. For instance this could be performed by bringing a multiplicityof contact pins into a plastic body, for example through an injectionmolding or casting method. The use of these techniques, however, iscumbersome and not very cost effective which is critical for an articlethat preferably should be discardable. The problem becomes even morecritical when moving in the direction of smaller pitches, for examplewell below 1 mm. The handling of individual needles or pins will beincreasingly difficult thus resulting in unacceptably high manufacturingcost.

[0026] Arrays of needles or needle-like configurations are of primaryinterest for the medical diagnosis and therapy of the skin or otherorgans and tissues of humans and animals. Such an array of electrodes,however, might also be useful for other configurations whenever it ispossible to establish electrical contact with the component to beinvestigated and when the determination of an impedance or electricalimage provides meaningful information. This typically applies tocomponents which do not have a hard outer surface because in this caseonly individual electrodes would establish an electrical contact.Therefore, components of interest are typically softer on their surfacelike elastomeric and similar components.

SUMMARY OF THE INVENTION

[0027] Accordingly, there is a need for an electrical signal sensingand/or signal application device for sensing electrical signals on asurface and/or for applying electrical signals to a surface, particularhuman or animal skin or other organs or tissues which device is providedwith an array of electrodes which can be reliably manufactured with avery small pitch in a cost efficient manner.

[0028] In a first aspect of the invention there is provided anelectrical signal sensing and/or signal application device for sensingelectrical signals on a surface and/or for applying electrical signalsto a surface, particularly of human or animal skin or other organs ortissues, wherein the device comprises

[0029] a substrate having first and second major surfaces,

[0030] a plurality of electrodes arranged on the first major surface ofthe substrate and projecting therefrom, each of the electrodescomprising a pointed contact end facing away from the substrate forcontacting the surface, and a base end facing towards the substrate, and

[0031] a plurality of first contact pads arranged on said first orsecond or both major surfaces of said substrate for electricalconnection to contact elements of an evaluation and/or driving means forevaluating the sensed electric signals and/or applying signals to saidelectrodes, said first contact pads being electrically connected to saidelectrodes,

[0032] wherein said first major surface of said substrate comprises, foreach electrode, a second contact pad said base ends of said electrodesbeing electrically and mechanically connected to said second contactpads, and

[0033] wherein each electrode is generated by bonding an electricallyconductive bonding wire to a second contact pad for generating athickened socket portion of said electrode comprising its base end, andby tearing the bonded bonding wire off the socket portion so as togenerate a pointed portion of said electrode comprising its pointedcontact end and projecting from the socket portion thereof.

[0034] On the first or second or both major surface of the substratethere is arranged a plurality of first contact pads for electricalconnection to contact elements of an evaluation and/or driving means forevaluating the sensed electric signals and/or applying signals to theelectrodes, the first contact pads being electrically connected to theelectrodes.

[0035] The first major surface of the substrate comprises, for eachelectrode, a second contact pad the base ends of the electrodeselectrically and mechanically connected to the second contact pads.

[0036] Each electrode is generated by bonding an electrically conductivebonding wire to a second contact pad for generating a thickened socketportion of the electrode comprising its base end, and by tearing thebonded bonding wire off the socket portion so as to generate a pointedportion of the electrode comprising its pointed contact end andprojecting from the socket portion thereof.

[0037] According to the invention, for the electrodes it is suggested toutilize a technology which is known from the electronic industry, namelyto use so-called ball bumps. Electronic chips and especially flip chipsare provided with external contact areas which by some means have to beconnected to a printed circuit board (PCB) and one way to achieve thisis to utilize these ball bumps. These are generated from extremely thinwires consisting of gold or gold alloys that have a diameter below 50microns, typically 25 microns. Through the use of a special equipmentthe ends of these wires are pressed on one of the components to beconnected, either the contact area in the chip or the correspondingcontact area in the PCB. Heat is applied electrically sufficient todeform the end of the thin wire and establish a mechanical andelectrical connection. Subsequently the wire is torn apart which createsa needle-like pointed configuration. After having provided all contactareas with these ball bumps the other component, either the flip chip orthe PCB, is then pressed onto the arrangement of the bumps. Thispressure is so high that the needle-like tips of the bumps are deformedso that also an electrical and mechanical connection is established.Needle-like configurations are not considered to be ideal and there areapproaches where it is attempted to avoid them or at least flatten them.

[0038] In contrary to the use of ball bumps in the electronic industryit is now suggested to take advantage of the needle-like pointed tips ofthe ball bumps. In the invention these bumps are created in exactly thesame manner as for the application in the electronic industry and inparticular are thermally or ultrasonically or both bonded to secondcontact pads of a flexible or rigid substrate. By this procedure anelectrode in the form of a so-called ball bump is generated on a secondcontact pad of the substrate wherein the ball bump electrode comprises athickened socket portion comprising the base end for electrically andmechanically contacting the second contact pad and a needle-like pointedportion comprising the pointed contact end of the electrode projectingfrom the socket portion. In the invention, the ball bumps are applied toe.g. a (rigid) printed circuit board or flexible circuit (i.e. thesubstrate) that has a pre-determined array of conductive paths or traceswhereby, however, the board or carrier could be any other configurationthat includes these paths. The bumps are attached to the end areas ofthese conductive paths and it is ensured that the pointed configurationis created without deformation for flattening them which in this case isa desired feature. It is advantageous to increase the size of the ballbumps which, however, depends on the practical application.

[0039] The substrate with the conductive paths may be mechanicallyrelatively unstable. For example it could consist of a flexible circuit,i.e. of a flexible layer having electrically conductive traces and padson it and may also comprise electric or electronic components for somereason. Therefore, it is advantageous to provide the system withadditional mechanical stability and, for example, the substrate of theconductive traces with the ball bumps applied onto could be supported bya plate which is appropriately attached to it providing the necessarymechanical stability. The plate can consist of plastic or metal providedthat the electrical circuits are not irritated. Instead of a plate alsoa completely solid component preferably consisting of plastic could beused.

[0040] The substrate can be rigid (e.g. PCB), flexible (e.g. flexiblecircuit layer) or a ceramic material. The conductive traces or paths mayextend over the surface of or through the substrate or both. In casethat the electrodes and the contact pads for connecting the substrate toa processing device are on different major surfaces of the substrate,the contact pads most preferably are aligned or flush with theelectrodes wherein the conductive paths directly extend through thesubstrate.

[0041] In another configuration a hand-held device could be used whichcomprises a handle that is provided at its distal end with an array ofelectrical contacts which for example could be a ball grid array (BGA).The handle at the other end is provided with the cable which iselectrically connected to the contact array, the cable guiding theelectrical information onto the evaluation unit consisting of a computerand a display.

[0042] Preferably, a discardable unit is created. This unit includes theconfiguration with the conductive traces like a PCB onto which the ballbumps are attached with means for providing the sufficient mechanicalstability and contact means for the electrical and mechanical connectionto a processing unit. This is particularly useful for the typicalapplications in the medical field where it is strongly advised to usesuch an electrode array for a single patient only. Therefore thediscardable portion should only contain the absolute minimum ofcomponents to fulfil the task.

[0043] In another aspect of the invention there is provided a method formanufacturing an electrical signal sensing and/or signal applicationdevice for sensing electrical signals to a surface and/or for applyingan electrical signal to a surface, particularly of human and animal skinor other organs or tissues, the method comprising the steps of

[0044] providing a substrate having first and second major surfaces,

[0045] forming first and second contact pads on the first or the secondor both major surfaces of the substrate,

[0046] providing electrically conductive traces at the substrate forelectrically connecting the first and second contact pads,

[0047] forming protruding electrodes onto the second contact pads bybonding a bonding wire to each of the second contact pads for generatinga socket portion of the respective electrode bonded to the secondcontact pad, and by tearing the bonded bonding wire off the respectivesocket portion so as to generate pointed portions of the electrodesprotruding from the socket portions thereof.

[0048] According to a third aspect of the invention the device asdescribed above is used for biomedical applications, in particular fordermal diagnostic and for sensing and/or stimulating biologic tissue ororgans or cells.

[0049] According to the invention there are provided an array of pointedelectrodes and a method of producing the same which are electricallyinsulated with respect to each other and which simultaneously areconnected to conductive traces of a substrate such as a printed circuitboard or a flexible circuit, whereby the manufacture of such anelectrode array including the connection means can be achieved in a costefficient manner.

BRIEF DESCRIPTION OF THE DRAWING

[0050] The invention will be described in more detail referring to thedrawing in which

[0051]FIG. 1 is a plan view onto a substrate having an array of ballbump electrodes according to a first embodiment of the invention,

[0052]FIG. 2 is a perspective view of a portion of the ball bumpelectrode array according to FIG. 1,

[0053]FIG. 3 is a perspective view onto a ball bump like electrode on alarger scale for illustrating the overall shape of the electrode,

[0054]FIG. 4 is a elevational view of the electrode of FIG. 3,

[0055]FIG. 5 shows an second embodiment of the device according to theinvention,

[0056]FIG. 6 shows an alternative embodiment of a device according tothe invention,

[0057]FIG. 7 shows a further embodiment of the device of the invention,and

[0058]FIG. 8 shows still another alternative embodiment according to theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0059]FIG. 1 shows a device 10 according to the invention and representsa view onto a circuit substrate 12 which can be a solid printed circuitboard or a flexible circuitry. On one of the major surfaces 14 of thesubstrate 12 an array of e.g. 8×8 electrodes 16 and electrode contactpads 18 of the substrate 12 can be identified, each of them beingconnected with its own conductive trace 20. It is to be noted that anarray of 8×8 electrodes is just a specific example and that it isadvantageous and desirable to increase the number of electrodes to, forexample, 16×16 corresponding to 256 individual electrodes. Even a highernumber could be used. This is possible and also realistic in view of thelow manufacturing cost when using the technology as suggested in theinvention. The electrodes 16 as such are provided as so-called ballbumps as described hereinbelow and used in the micro-electronic industryfor connecting chips using the flip chip technology.

[0060] In FIG. 2 a perspective view of a part of the electrode array ona larger scale is shown. Each conductive trace 20 leads to a firstcontact pad 22 (see FIG. 1) which by some connection means isconnectable to an electronic device for generating and evaluatingelectrical signals to be applied to or sensed by the individualelectrodes 16. These electrical signals can represent impedances,currents, voltages, potentials, AC or DC or impulse signals. Theconnection means can comprise a ball grid array (BGA), a land grid array(LGA) or contact pins and the like.

[0061]FIGS. 3 and 4 show in more detail the design and construction of aball bump electrode 16. This electrode 16 comprises a thickened socketportion 24 having a base end 26 for electrically and mechanicallyconnecting the socket portion 24 to an electrode contact pad 18. Theshape of the socket portion 24 looks like a flattened ball having arounded periphery 28, wherein the lower side 30 of the socket portion 24being flat so as to contact the second contact pad 18. In the middlefrom the upper side 32 of the socket portion 24 there protrudes apointed portion 34 having a pointed end 36. This pointed portion 34contacts the surface (human or animal skin or organ or tissue or cell)to be measured or investigated.

[0062] It is to be noted that FIGS. 3 and 4 schematically show the ballbump which as of yet is used in the flip chip technology for connectingchips to a circuitry layer with the structured side of the chip facingthe circuitry layer. In particular the pointed portion 34 can be longerand more needle-like or sharper or both than depicted. The relatedtechnology for generating such bumps and the typical use is described ina number of articles, for example “Flip Chip Attachment Using MechanicalBumps” by J. Eldring et al., 1994, ITAP & Flip Chip Proceedings, pages74-81, “Flip Chip Attachment Using Non-Conductive Adhesives and GoldBall Bumps” by R. Aschenbrenner et al. from the Technische UniversitatBerlin, Forschungsschwerpunkt Technologien der Mikroperipherik, TIB4/2-1, or “Single Chip Bumping” by Matthias Klein et al., TechnicalUniversity of Berlin, Center of Microperipheric Technologies. The latterarticle describes the typical technology in more detail. Thin wires ofAu98Pd for example, with diameters between 18 and 33 micrometers aregrabbed by a wire clamp and pressed on the contact area to be connected.These contact areas can either be located on the flip chip or thecomponent, comprising the conductive paths such as a PCB. This can bedone utilizing a conventional ball-wedge bumping process, namely a wirebonder, for example available from F&K Delvotech Bondtechnik GmbH,Germany. The wire is passed through a capillary tube which forms thewire clamp and an electrical discharge is applied which forms a ballestablishing the electrical and mechanical connection to the contactarea to be connected. This is identical to the well known wire bondingtechnique. In a second step, however, the wire is torn off whereby it isensured that this rupture occurs within the heat effective zone wherethe grain structure of the wire is coarser compared to the non-affectedstate. The rupture causes a lengthening of the wire with a significantsimultaneous reduction of its diameter until it becomes so thin that itruptures. In this way a pointed configuration is obtained which actuallyfor the intended purpose of the electrical connection is undesirable.

[0063] The effect of such a process can be seen from FIG. 3 which showsa perspective view of such a mechanically applied gold stud bump on analuminium pad. FIG. 4 shows a cross-sectional view showing the typicaldimensions. The overall diameter D of the ball bump ranges between 40and 105 microns. The actual con-tact area B (base end 26) on the contactpad 18 to be contacted is typically 80 percent of the dimension D. Theheight h of the socket portion 24 as shown in FIG. 4 typically rangesbetween 12 and 65 microns. The height H is about 10 microns larger. Theoverall height h′ of the ball bump typically corresponds to the diameterD of the entire ball bump. In this application heights of 100-200microns are advantageous for an optimum penetration of the pointedportion 34 and the pointed end 36 into the skin. Namely, the outermostportion of the skin typically has a thickness of around 100 micronswhich should be penetrated to establish a good electrical contact. Theactual pointed end 36 occurs in the upper part, namely in that part ofthe overall height h′ that exceeds H. The dimension b is around half to⅓ of the height h of the socket portion 24. The above mentioned articlerefers to specific details of the ball bump in flip chip technologyapplication. For example it has been shown that the connection to thecontact pad 18 is sufficiently stable. Shear values in the area of 43-60cN/bump have been observed. Alternative alloys are PbSn2, PbSn61, andSnAg3 and relatively pure gold itself.

[0064]FIG. 5 shows another embodiment of the device according to theinvention. This embodiment is rather similar to that of FIGS. 1 and 2.The difference between these embodiments can be seen in the fact that inthe embodiment of FIG. 5 the conductive traces 20 extend through thesubstrate 12 in the thickness direction thereof with the end surfaces ofthe conductive traces 20 laying in the first and second major surfaces14 of the substrate 12 forming the second contact pads 18 and the firstcontact pads 22.

[0065]FIG. 6 shows an alternative embodiment having is a configurationthat in principle is similar to the one depicted in FIGS. 1 and 2,however, arranged in a non-flat configuration. Also here ball bumpelectrodes 16 have been applied to contact pads of the flexiblesubstrate 12. The substrate 12 is supported by a metal 38 stiffenerwhich is arranged so that the conductive traces 20 cannot be irritatedas they are on the side 14 of the substrate 12 facing away from themetal stiffener 38. The contact area with the contact pads 22 can be azebra strip, a ball grid array (BGA), or a land grid array (LGA) 40.

[0066]FIG. 7 shows an embodiment which is very similar to the one shownin FIG. 6 with the essential difference that instead of providing ametal plate as a stiffener a plastic body 42 is applied which is solidin itself the whole system, however, being essentially identical to theone shown in FIG. 6.

[0067]FIG. 8 shows an alternative embodiment in which the component withthe ball bump electrodes 16 is configured in a way to be discardable.The ball bump electrodes 16 are applied to a flexible circuit layersubstrate 12 having BGA or LGA contact areas 44. The substrate 12 isfixed onto a plastic or metal support part 46. The discardable component48 can be attached to a hand-held device 50. Accordingly this device 50has to comprise mechanical features like snapping means and the like(not shown) which allow to fix the discardable component 48 onto thehand-held device 50 keeping it in a position stable enough for theintended evaluation such as the generation of an electrical or impedanceimage of a skin portion of a patient. The hand-held device 50 includesthe handle 52 as such which can be of a pistol type. Furthermore, itincludes a cable 54 connected to the connecting means 56 of thehand-held device 50 for connection to the BGA or LGA contact areas 44 ofthe discardable component 48. At its other end (not shown) the cable 54is connected or connectable to an evaluation unit, typically a computerand a display unit.

1. An electrical signal sensing and/or signal application device forsensing electrical signals on a surface and/or for applying electricalsignals to a surface, particularly of human or animal skin or otherbiological organs or tissues, comprising a substrate (12) having firstand second major surfaces (14), a plurality of electrodes (16) arrangedon the first major surface (14) of said substrate (12) and projectingtherefrom, each of said electrodes (16) comprising a pointed contact end(36) facing away from said substrate (12) for contacting the surface,and a base end (26) facing towards said substrate (12), and a pluralityof first contact pads (22) arranged on said first or second or bothmajor surfaces (14) of said substrate (12) for electrical connection tocontact elements of an evaluation and/or driving means for evaluatingthe sensed electric signals and/or applying signals to said electrodes(16), said first contact pads (22) being electrically connected to saidelectrodes (16), wherein said first major surface (14) of said substrate(12) comprises, for each electrode (16), a second contact pad (18) saidbase ends (26) of said electrodes being electrically and mechanicallyconnected to said second contact pads (18), and wherein each electrode(16) is generated by bonding an electrically conductive bonding wire toa second contact pad (18) for generating a thickened socket portion (24)of said electrode comprising its base end (26), and by tearing thebonded bonding wire off the socket portion (24) so as to generate apointed portion (34) of said electrode (16) comprising its pointedcontact end (36) and projecting from the socket portion (24) thereof. 2.The electrical signal sensing and/or signal application device accordingto claim 1, wherein said substrate (12) is flexible.
 3. The electricalsignal sensing and/or signal application device according to claim 1,wherein said substrate (12) is rigid.
 4. The electrical signal sensingand/or signal application device according to any one of claims 1 to 3,wherein said second contact pads (18) are electrically connected to thefirst contact pads (18) of said substrate (12) via electricallyconductive traces (20) arranged on said substrate (12).
 5. Theelectrical signal sensing and/or signal application device according toany one of claims 1 to 3, wherein said first contact pads (22) arearranged on said second major surface of said substrate (12) and flushwith the second contact pads (18) and are electrically connected to saidsecond contact pads (18) by conductor portions extending through saidsubstrate (12).
 6. The electrical signal sensing and/or signalapplication device according to any one of claims 1 to 5, wherein saidsocket portions (24) of said electrodes (16) are connected to saidelectrode contact pads (18) by thermal bonding or ultrasonic bonding orboth.
 7. A method for manufacturing an electrical signal sensing and/orsignal application device for sensing electrical signals to a surfaceand/or for applying an electrical signal to a surface, particularly ofhuman or animal skin or other biological organs or tissues, said methodcomprising the steps of providing a substrate (12) having first andsecond major surfaces (14), forming first and second contact pads(22,18) on said first or said second or both major surface (14) of saidsubstrate (12), providing electrically conductive traces (20) at saidsubstrate (12) for electrically connecting said first and second contactpads (22,18), forming protruding electrodes (16) onto said secondcontact pads (18) by bonding a bonding wire to each of said secondcontact pads (18) for generating a socket portion (24) of the respectiveelectrode (16) bonded to said second contact pad (18), and by tearingsaid bonded bonding wire off said respective socket portion (24) so asto generate pointed portions (34) of said electrodes (16) protrudingfrom said socket portions (24) thereof.
 8. The method according to claim7, wherein said bonding wire is thermally bonded or ultrasonicallybonded or both to said second contact pads (18) of said substrate (12).9. Use of the device of any one of claims 1 to 6 or the devicemanufactured according to claim 7 or 8 for biomedical applications, inparticular for dermal diagnostic and for sensing and/or stimulatingbiological tissue or organs or cells.